This invention relates to the field of safety alarms, and more particularly to alarms for detecting the presence of a dangerous condition in a monitored space.
As known, there are several different types of safety type alarms, including smoke alarms, heat alarms, and carbon monoxide detector alarms. While each of these differ in the alarm condition they detect, they all perform common alarm signaling protocols to give notice of the detected condition. The alarm notice is provided locally to warn occupants within or near the space, and may be provided to a remote monitoring location by electronic communication. To ensure adequate local notice to those in or near the monitored space, the local alarm is provided with audible and visible annunciation, using horns and lamps. Depending on the type condition being detected, the alarm protocols differ in their excitation pattern and frequency. They may also differ in their audible tones and in the intensity of their visible warning.
In locations where there are more than one installed alarm, such as in a multi-room residence where alarms may be installed in each of several floors, as well as in each of several spaces on a floor, it is well known to functionally interconnect the smoke alarms in a network to allow all units to annunciate an alarm condition detected by any one of the networked units. This provides broadcast notice of the alarm to every occupant, no matter where they are within the residence or building. One characteristic of this networked arrangement, however, is that it is not possible to determine which of the interconnected units detected the condition and originated the alarm after the alarm condition has concluded. It is advantageous to know which of several units is the originating unit, especially in the event of a false alarm condition, where it is desirable to replace only the defective unit, which will minimize replacement unit cost and needless time spent for the services of a contractor or electrician. Without an ability to determine which of the units originated the false alarm, all units must be replaced.
U.S. Pat. No. 5,933,078, by T. J. O""Donnell, issued Aug. 3, 1999, solved this problem for common residential applications by providing a smoke alarm unit that latches the unit""s visual alarm annunciator in the xe2x80x9conxe2x80x9d, or illuminated state, whenever the unit detects an alarm condition. This occurs only within the unit which detects the alarm condition. All of the other networked units annunciate the alarm, but when the alarm condition is cleared only the originating unit continues to display a visible alarm state. This allows for immediate identification of the alarm originating unit within the network, and for its replacement in the event of a false alarm.
One problem with this self identifying unit is that the visual indicator is constantly lighted in this latched state. Ideally, the building occupant would notice this signal in a relatively timely manner, but oftentimes the condition of smoke alarms, unless sounding their audible alarm, go unnoticed. Since this condition is capable of accelerating the discharge of the battery of a battery powered unit, or the back-up battery of AC/DC model smoke alarms which use the back-up battery to power the visual indicator, its use may be limited to smoke alarms which are AC powered. To broaden the use of this feature to battery powered smoke alarms it is necessary to develop a method of providing the origination function in a manner which decreases the service life of the battery by only a small amount.
The object of the present invention is to provide improved methods and apparatus for displaying the alarm origination feature in a smoke alarm, in a manner which minimizes the load current drawn from the smoke alarm power source. Another object of the present invention is to provide improved visual notice of an alarm origination condition to an observer. Still another object of the present invention is to provide a useful and non-ambiguous hybrid signal when a combination of notice of alarm origination and low-battery signal is present.
According to one aspect of the present invention, the visual annunciation of an alarm origination condition is provided by pulsed modulation of the visual annunciator, to produce an intermittent pattern of lighted pulses. In further accord with this aspect of the present invention, the pulsed width excitation of the visual annunciator is at an average duty cycle which is no greater than approximately 0.075%. In still further accord with this aspect of the invention, the pulsed width excitation of the visual annunciator is at an average duty cycle which is no less than approximately 0.025%.
According to another aspect of the present invention, the visual pattern for notification of an alarm origination was chosen to broadly emulate the sequence of three pulses of periodicity of the audible temporal pattern specified by the Underwriter""s Laboratories Standard UL217 for alarm annunciation, thereby providing improved recognition of the pulsed visual alarm origination condition on the basis of its association with the pattern of the audible annunciation of an actual alarm condition.
In accordance with a still further aspect of the present invention, a low battery annunciation is provided as one of a plurality of prioritized state conditions of the sensor alarm, with the low battery annunciation being encoded with a distinct code which allows it to be readily distinguishable from the other state condition alarms of the sensor alarm.
In the sensor alarm of the present invention a hybrid signaling condition is defined whereby the visual indicator (LED) uses three sequential flashes to show an alarm origination condition, and the audible indicator (the horn) xe2x80x9cchirpsxe2x80x9d (if enabled) approximately once per minute to declare a low-battery condition. Upon relief of either condition, the smoke alarm""s integrated circuit (IC) functional specification requires that the particular indicators return to their independent state (either only low-battery condition or only post-alarm condition).